1. Field of the Invention
This invention relates to pointer device for an instrument, such as a speedometer, in a vehicle, and more particularly to a pointer device for an instrument wherein the pointer is self-illuminating when light is radiated into the pointer.
2. Background
A conventional pointer device of this type includes a rotatable pointer designed to point to a graduated mark on a scale plate as an indication of a measured parameter. The pointer is made of a transparent material such as acrylic resin. A light source is provided at the base of the pointer, or alternatively, light from a light source is directed to the base of the pointer, so that light emitted from the light source is transmitted to the tip of the pointer from the base, thereby illuminating the entire pointer.
While the material of the above-described conventional pointer is transparent, it is a pure resin material. Therefore, the light decreases in intensity as it advances toward the tip of the pointer, as a result of which the base is illuminated to a greater degree than the tip and correspondingly, the pointer is not uniformly illuminated. In order to eliminate this difficulty; that is, in order to uniformly illuminate the pointer from the base to the tip, a variety of methods have been proposed in the art. However, in these methods, the degree of illumination is based on the minimal illumination thereby reducing overall illumination of the pointer body. Hence, none of the methods are effective in illuminating the pointer with a sufficiently high intensity.
In order to overcome this difficulty, there has been proposed a pointer which illuminates with a high intensity. For instance, a cold cathode ray tube is employed as a pointer, or a number of light emitting diodes are arranged in parallel to form a pointer. These pointers are advantageous in that they are highly illuminating because they are made of a light source or a plurality of light sources. However, these pointers are still disadvantageous in that they are expensive, and relatively heavy. Therefore, the load applied to the movement for driving the pointer must be relatively large, and the movement is unavoidably bulky.